iOS Hands First day

////main.m//Lessionpointer////Created by Laouhn on 15/7/24.//Copyright (c) 2015 Chi Hai Tao. All rights reserved.//#import<Foundation/Foundation.h>voidJiaohuan (int*a,int*b) {    *a = *a^*b; *b = *a^*b; *a = *a^*b;}intMainintargcConst Char*argv[]) {    //pointer variable: The variable that stores the address    /** * Pointer defines the function of the data type, tells the system what type of pointer//pointer variable is defined, and the function of the data type (take int as an example) 1. Tell the system I am an int type pointer 2. In the pointer The operation is that the number of bytes per offset is int-4 bytes 3. The pointer controls the number of bytes, int controls 4 bytes*/    /** int a = 10; int *p = null;//pointer variable p char *q = NULL;     The data type of the pointer q is: char *;     Usually we call the pointer, is actually the pointer variable, the pointer is stored in the address//pointer variable address of the output printf ("%p\n", p);     The number of bytes that the pointer variable occupies: Only the number of system operating system bits, 32 os 4 bytes, 64-bit operating system 8 bytes printf ("p =%lu\n", sizeof (p));          printf ("q =%lu\n", sizeof (q));     Fetch operator: & p = &a;     printf ("%p\n", p);     printf ("%p\n", &a);                    The value operator *//PRINTF ("%d\n", *p);          The assignment of a pointer variable: The pointer is redirected, which is the process of re-copying the pointer variable.     Pointer operations: Only add and subtract operations.     printf ("%d\n", * (p+1));          printf ("%p\n", p+1);     printf ("q+1 results after output%d\n", * (q + 1)); *///int a = ten;//int *p = &a;//*p = +;//    //*p on the left side of the equals sign is the assignment to the address stored in P, otherwise it is a value operation//    //int *p = NULL; *p is defined as a pointer variable when defined.//printf ("%d\n", a); //Pointers and Arrays    /** * int a[] = {9, 5, 2, 7};          The array name is the first address of the array, but the array name is a constant address printf ("%p\n", a);                    printf ("%p\n", &a[0]);          int *p = A;     printf ("%d\n", *p);          Pointer offset to pointer type about printf ("%d\n", * (P + 1));          printf ("%d\n", p[1]);          printf ("%d\n", * (p + 1 + 1));               printf ("%d\n", * (p + 1 + 1 + 1));     printf ("%d\n", *a);     printf ("%d\n", * (a+1));          printf ("%-----d\n", a[1]);     int b[] = {3, 8, 4, 9};     p = b;//pointer to//a = B;a is a constant, cannot be assigned, and the pointer is a variable that can be redirected (re-assigned).          Array type, does not match pointer type, what is the problem?     int b[] = {256, 5, 2, 7};     int *p = b;     for (int i = 0; i < 4; i++) {printf ("%d", * (P + i));          }//printf ("%d\n", * (q + 1));     Char str[] = "IPhone";     char *p = str;     Output string by pointer printf ("%s\n", p);     Change h to H, directly through the address of the value inside the change is the value operator * (P + 2)-= 32;          printf ("%s\n", p); In this case, Q stores the address of the constant area, and the contents of the constant area are not allowed to be modified. Remember!!???     (Alt shift +k) char *q = "IPhone"; (q + 2) = ' H ';               printf ("Q's address%p\n", q);     Calculates the length of a string by using a pointer.     Char str[] = "IPhone";     int i = 0;     char *p = str;     while (* (P + i)! = 0) {i++;           } printf ("%d", I);*/    //Array of strings//char strarray[][20] = {"IPhone", "IPod", "IPad", "IWatch"}; //printf ("%s\n", strarray[0]); //an array of pointers, which are stored as addresses .//char *str[] = {"IPhone", "IPod", "IPad", "IWatch"};//    //printf ("++++%lu", sizeof (str));//for (int i = 0; i < 4; i++) {//        //printf ("%p", Str[i]);//printf ("%s", Str[i]);//    }//printf ("\ n"); //printf ("%p\n", &str[0]); //char p[] = "DDDDD"; //array of the above pointers, sorted in ascending order//Str[0] Stores the first address of the iphone//Str[1] The first address of the ipod is stored//Str[2] is the ipad's first address .//Str[3] Iwatch's first address is stored .    /** for (int i = 0, i < 4-1; i++) {for (int j = 0; J < 4-1-I; j + +) {if (strcmp (str)     [j],str[j+1]) >0) {//* (P + 2) p[2]//Compare the contents, the position of the address in the array is exchanged char *temp =str[j];     STR[J] = str[j + 1];     Str[j + 1] = temp; }}} for (int i = 0; i < 4; i++) {//printf ("%p", Str[i]); The elements in the output array printf ("%s", Str[i]);//output array element, corresponding to the contents of the address}//string array char str[4][20] = {"IPhone", "IPod", "IPad", "          IWatch "};     An array of pointers that stores the stack space address char *strarray[4] = {str[0], str[1], str[2], str[3]};     for (int i = 0; i < 4;i++) {printf ("%p", Strarray[i]);      } printf ("\ n");    An array of pointers that stores the address of the constant space char *str1[4] = {"IPhone", "IPod", "IPad", "IWatch"};    for (int i = 0; i < 4;i++) {printf ("%p", Str1[i]); }     */    //Pointers and Functions    intA =5; intb =6; Jiaohuan (&a,&b); printf ("a=%d,b=%d", A, b); return 0;}

iOS Hands First day